Polygon mirror scanner having an easily replaceable bearing

ABSTRACT

A polygon mirror scanner is disclosed, comprising a rotor having a rotating shaft, a polygon mirror having a regular prism and having a mirror surface on each side thereof, and a magnet; a bearing device, rotatably bearing the rotor, having a radial bearing, a thrust bearing, and a stator yoke; and a stator having a coil facing the magnet with a predetermined distance therebetween, wherein the radial bearing and the thrust bearing are exchangeable at the end of their useful life while maintaining a desired level of high precision and tolerances for proper and efficient operation of the polygon mirror scanner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This document is a divisional of U.S. Application Ser. No. 10/665,551,filed Sep. 22, 2003, and is based upon, claims priority, and containssubject matter related to Japanese Patent Application No. 2002-276265filed Sep. 20, 2002. The contents of both applications are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polygon mirror scanner for lightwriting for use in digital copiers, page printers, and the like.

2. Discussion of the Background

FIG. 4 is a schematic view illustrating a cross section of aconventional polygon mirror scanner. A rotary polygon mirror 1 has adisc-shaped plane polygon (an equilateral hexagon in FIG. 4), acylindrical rotor 3 below the rotary polygon mirror 1, a head 1 a abovethe rotary polygon mirror 1 in the center thereof and six side faces 1 bon the periphery of the rotary polygon mirror 1.

The six side faces 1 b on the periphery of the rotary polygon mirror 1are mirror-finished smooth light reflection faces (mirror faces). Thecenter of the head 1 a, i.e., a center of gravity of the equilateralhexagon, has a hole, where a rotating shaft 2 fitted to the rotarypolygon mirror 1 is inserted. In addition, the rotating shaft 2 has acurved surface at both ends thereof.

A magnet 4 has a cylindrical shape having an outer diameter which isalmost equal to an inner diameter of the rotor 3, and is fixed insidethe rotor 3 so as to be concentric with the rotating shaft 2 to form arotor 10 for the polygon mirror scanner.

A bearing device 20, supporting the rotating shaft 2 of the rotor 10,includes a radial bearing 21, supporting the rotating shaft 2, a thrustbearing 22, receiving a thrust load of the rotating shaft 2, and astator yoke 23, supporting the radial bearing 21. The radial bearing 21is formed of a slide bearing, such as a bearing including an oil, andfixed by being pressed into or bonded to an inner circumferentialsurface of the stator yoke 23.

The thrust bearing 22 is formed of a slide bearing, e.g., a resin platesuch as polyimide having good slidability and abrasion resistance, andfixed by being pressed into or bonded to a concave part on the bottom ofthe inner circumferential surface of the stator yoke 23. The bearingdevice 20 is vertically fixed to a plane surface of a control base plate32, and a coil 31 is fixed on a peripheral surface of the bearing device20 to form a stator 30.

The coil 31 may be fixed on the control base plate 32. In addition, aperipheral cylindrical surface of the coil 31 faces a peripheralcylindrical surface of the inner circumferential and cylindrical surfaceof the magnet 4, while maintaining a predetermined clearance.Electricity from the control base plate 32 to the coil 31 drives therotary polygon mirror 1 to rotate around the rotating shaft 2.

Conventionally, a rotary polygon mirror for use in a polygon mirrorscanner for copiers, and like devices is constituted of a flat memberhaving a mirror finished surface on its circumference. The mirrorfinished rotary polygon mirror is assembled with a rotor and a magnet toform a rotor for a scanner motor, i.e., a rotor for the polygon mirrorscanner. The rotary polygon mirror is assembled with a rotating shaft, arotor yoke, and a magnet to form a rotor for the polygon mirror scanner.

A stator works as a motor driving the rotary polygon mirror to rotate ascanning light beam, wherein a coil is arranged facing the magnetinstalled in the rotor with a predetermined space and a rotating shaftof the rotor is supported on a base plate on which a controllerswitching an energizing level of the coil is located.

Due to recent increasing environmental concerns, it is essential thatelectrical and mechanical products are reused and recycled. Therefore,individual components for digital copiers, page printers, and othersimilar devices need to be reused and recycled.

It has been said that a rotating shaft and a bearing for a polygonmirror scanner for light writing for use in the digital copiers, pageprinters, and the like can only be reused as a recycled metallicmaterial or disposed of because, over time, they cannot avoid abrasionand damage due to their extended use.

However, a rotor including a rotary polygon mirror of a polygon mirrorscanner for light writing, a rotating shaft, a rotor and a magnet in abody has less abrasion and damage of the rotating shaft due to itsextended use. On the other hand, the bearing cannot avoid abrasion anddamage due to its extended use.

Therefore, when the bearing comes to the end of its useful life, thepolygon mirror scanner has to be exchanged as an assembly, although someof its components are still in a good and useful condition. In addition,a precise modification of the rotary polygon mirror of the rotorrequires a significant amount of time and energy; therefore, the rotarypolygon mirror has to be reused.

Japanese Laid-Open Patent Publication No. 2000-41359 discloses a methodof removing only a rotating shaft from a motor frame and recycling othermembers thereof.

In the above-mentioned conventional polygon mirror scanner for lightwriting, the bearing is abraded by a contact of the rotating shaft whenthe rotation stars and stops because the rotating shaft, which is acenter of rotation, is formed of a material harder than that of thebearing.

In addition, over an extended period of use, the rotational loaddeteriorates as a result of, as for example, a loss in lubrication. Inthese situations, the polygon mirror scanner takes longer to reach astable rotational high-speed and experiences operational difficulties,including an irregular rotation and difficulty in maintaining a desiredhigh-speed. These operational problems result in an increase of electricpower consumption and a reduction in efficiency of the polygon scannermirror.

Therefore, when the bearing comes to the end of its useful life, thepolygon mirror scanner is exchanged as an assembly although some of itscomponents have not come to the end of their useful lives, resulting inthe unnecessary replacement of the good components.

In addition, it is not possible to replace the bearing without replacingthe stator yoke into which the bearing is pressed, resulting inalteration and/or loss of the required high vertical precision or tighttolerances between the stator yoke to and the bottom surface of themotor circuit board due to current repair methods, thus, it becomesdifficult to reach the needed high rotational speed and desired highefficiency for the polygon mirror scanner.

For at least the foregoing reasons, a need exists for a polygon mirrorscanner having a bearing that can be easily replaced at the end of itsuseful life, while continuing to use other components in the mirrorassembly that are still in good operating condition and maintaining therequired high precision and tight tolerances for proper and efficientoperation of the mirror assembly.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a polygonmirror scanner having a bearing that is easily exchangeable at the endof its useful life while maintaining a desired level of high precisionand tolerances for efficient operation of the polygon mirror scanner.

Briefly, this, and other objects of the present invention, ashereinafter will become more readily apparent, can be attained by apolygon mirror scanner comprising:

a rotor, comprising:

-   -   a polygon mirror having a mirror surface on each aspect of a        regular prism; and    -   a magnet

a bearing device bearing the rotor so as to be rotatable, the bearingdevice comprising:

-   -   a radial bearing;    -   a thrust bearing; and    -   a stator yoke, and

a stator, comprising:

-   -   a coil facing the magnet with a predetermined distance        therebetween,

wherein the radial bearing and the thrust bearing are exchangeable.

These and other objects, features, and advantages of the presentinvention will become apparent upon consideration of the followingdescription of the preferred embodiments of the present invention takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features, and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the detailed description when considered in connectionwith the accompanying drawings in which like reference charactersdesignate like corresponding parts throughout and wherein:

FIG. 1 is a schematic view illustrating a cross section of an embodimentof the polygon mirror scanner of the present invention;

FIG. 2 is a schematic view illustrating a cross section of a modifiedembodiment of the radial bearing in the embodiment of the polygon mirrorscanner in FIG. 1;

FIG. 3 is a schematic view illustrating a cross section of anotherembodiment of the polygon mirror scanner of the present invention; and

FIG. 4 is a schematic view illustrating a cross section of aconventional polygon mirror scanner.

DETAILED DESCRIPTION OF THE INVENTION

Generally, the present invention provides a polygon mirror scannerhaving a bearing that is easily replaced at the end of its useful lifewhile maintaining a desired level of high precision and tolerances forefficient operation of the polygon mirror scanner.

Hereinafter, an embodiment of the present invention will be explained indetail, referring to the drawings. In FIG. 1, like components have thesame numerals as those of the conventional polygon mirror describedabove in FIG. 4.

A bearing device 20 has a convex cylindrical shape, including a statoryoke 23 having a cylindrical central hole concentrically and axiallywith a rotating shaft 2 and forming an inner circumferential screw 23 bbelow, a radial bearing 21 having a cylindrical central holeconcentrically and axially with a rotating shaft 2 and forming a collar21 a on a peripheral surface thereof in a body and a cylindrical fixingscrew 41 fixing the radial bearing 21.

In addition, a peripheral screw 41 a is formed on a peripheral surfaceof the fixing screw 41, and a top surface thereof has a thrust groove 41b on which a thrust bearing 22 is fixed.

The radial bearing 21 is inserted into the cylindrical central hole 23Awhich is formed in the stator yoke 23 and concentrically and axiallywith the rotating shaft 2 from beneath. A top surface (standard portion)of the collar 21 a formed with the radial bearing 21 in a body iscontacted with a standard surface 23 a (standard portion) formed on aninner circumferential surface of the stator yoke 23 to fix the radialbearing 21 vertically to a control base plate 32.

In the present invention, bearings 21 and 22 are detachable from thestator yoke 23. In addition, the bearings 21 and 22 are fixed byscrewing the peripheral screw 41 a into a female screw of the statoryoke 23 after being inserted into the central hole 23A therein.

FIG. 2 is a schematic view illustrating a cross section of a modifiedembodiment of the radial bearing in the embodiment of the polygon mirrorscanner in FIG. 1. As FIG. 2 shows, an upside standard portion 21 b ofthe radial bearing 21 is contacted with an inner circumferentialstandard 23 c on an upside inner circumferential surface of the statoryoke 23 to fix the radial bearing 21 vertically to a control base plate32.

A thrust bearing 22 is fixed on a thrust groove 41 b formed on a topsurface of a fixing screw 41 by being pressed or adhered to the thrustgroove 41 b. The radial bearing 21 is fixed by screwing the fixing screw41 into a cylindrical inner circumferential screw 23 b formed on thebottom of the stator yoke 23.

FIG. 3 is a schematic view illustrating a cross section of anotherembodiment of the polygon mirror scanner of the present invention.

A bearing device 20, having a convex cylindrical shape, comprises astator yoke 23, having a cylindrical central hole concentrically andaxially with a rotating shaft 2 and forming a circumferential bearingbuilding screw 23 d on top and a thrust groove 41 b on the bottom; aradial bearing, having a cylindrical central hole concentrically andaxially with a rotating shaft 2 and forming a circumferential bearingscrew 21 c on a peripheral surface thereof on top and a building groove21 e on a top surface thereof, and a thrust bearing 22 fixed on thethrust groove 41 b.

The radial bearing 21 is inserted into the cylindrical central hole,which is formed in the stator yoke 23 and concentric and axial with therotating shaft 2 from above. The radial bearing 21, forming the bearingscrew 21 c, is screwed into the cylindrical bearing building screw 23 d(inner circumferential screw) until the radial bearing 21 is contactedwith a bearing stopper 23 c. Thus, the radial bearing 21 can bevertically fixed to a control base plate 32. In addition, the buildinggroove 21 e on a top surface of the radial bearing 21 is a tool groovewhen the radial bearing 21 is screwed into the inner circumferentialscrew 23 d. When the screws 21 c and 21 d formed on the radial bearingis screwed into the screw 23 d formed on the stator yoke 23, the radialbearing 21 is easily detachable with the stator yoke 23.

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth in the claims herein.

1. A bearing device, having a convex cylindrical shape, comprises: astator yoke having a cylindrical central hole concentrically and axiallywith a rotating shaft and forming a circumferential bearing buildingscrew on top and a thrust groove on the bottom, a radial bearing, havinga cylindrical central hole concentrically and axially with the rotatingshaft and forming a circumferential bearing screw on a peripheralsurface thereof on top and a building groove on a top surface thereof,and a thrust bearing fixed on the thrust groove, wherein the radialbearing is inserted into the cylindrical central hole in the statoryoke, the radial bearing is attached to a cylindrical bearing buildingscrew, and the building groove on the top surface of the radial bearingis a tool groove when the radial bearing is attached to thecircumferential screw, and, when the screws formed on the radial bearingare attached to the screw formed on the stator yoke, the radial bearingis detachable from the stator yoke.
 2. The bearing device of claim 1,further comprising the radial bearing being configured to contact abearing stopper, allowing the radial bearing to be vertically fixed to acontrol base plate.
 3. The bearing device of claim 1, further comprisinga standard portion comprising the control base plate having a standardsurface, wherein the standard portion is configured to verticallystabilize the radial bearing using the standard surface of the controlbase plate.
 4. The bearing device of claim 3, wherein the surface of thecylindrical central hole serves as the standard surface of the standardportion.
 5. The bearing device of claim 3, wherein the radial bearinghas a collar on a peripheral surface thereof serving as the standardsurface of the standard portion.